About a week ago, I did the remove, sharpen and re-install exercise on my jointer blades for the first time. I rented the magnetic jig from my sharpening shop only to find that they were designed for industrial sized machines -- meaning the diameter of my blade holder was a bit too small to have the magnets grab the holder securely... the rental was a waste.

I did come up with a suitable "trick".

It is in two steps:

Set all three blades level and in a perfect circle.

Set the outfeed table flush to the arc scribed by the blades.

Then:

First mount one blade using your eye to align the top of the cutting arc with the outfeed table. Tighten the bolts, but not too much. Use a good straight edge (I used the blade from my square) on the outfeed table. Rotate the blade (backwards) so the top of the arc is below the straight edge protruding from the outfeed table. Place the straight edge near one end of the blade. (You will later align the other end, making the blade "straight" with respects to the outfeed table.) Place a mark on the straight edge then place the straight edge on the outfeed table with the mark (perfectly) aligned with the edge of the outfeed table closest to the blade. Holding the straightedge very lightly, slowly rotate the blade in the normal cutting direction. The blade will pick up the straight edge and move it forward slightly (about 1/8" in my case). Holding the straightedge carefully, mark the straightedge where the outfeed table intersects the edge. You should have two marks on the straight edge, about 1/8" apart.

Move your straight edge to the other end of the blade, set the first mark in alignment with the edge of the outfeed table. Move the blade backwards so it is below the straight edge (lift the ruler). As you rotate the blade forwards, it will lift the ruler again, moving it forwards. If the second mark aligns with the outfeed table (as it did on the first), you have successfully aligned the first blade -- tighten bolts carefully and recheck by testing both ends of the blade again. If the marks are "off", you have to raise or lower the blade according to what the second mark tells you. If this end of the blade moves the mark more than the other end did, this end is high, lower the blade. (I tapped it very lightly with a piece of hardwood.) If this end of the blade move the mark less than the other end, this end of the blade is low, pry it up a bit (I used a screwdriver.)

Repeat 1a and 1b for the other blades (mine had three) Once all blades create the same movement in the ruler -- you have a perfect circle set up with the blades.

Now you may have to adjust the outfeed table to ensure that zero is truly no cuts off the wood.

Finally, if you want to check that you have really set it up properly, shake some chalk-line chalk onto each blade then joint a piece of wood that is as large as your jointer will take, removing a tiny bit of wood. (If you take too much, you will obscure any tiny differences that might be in your setup.) Chalk left on the knives anywhere indicates that you have to do it all again, you must have gotten tired, or shifted the knives while tightening the bolts.